The present application relates to methods of conversion of plant oils into high molecular weight natural plant oil polyols that can be used as raw materials in the manufacture of polyurethanes.
The manufacture of polyurethanes from polyisocyanates requires readily available coreactants. These coreactant materials are known in the art as polyols. Polyols may be defined as reactive substances, usually liquids, that contain at least two isocyanate-reacting groups attached to a single molecule. Such isocyanate reacting groups (hydroxyl radicals) are also known as “active hydrogen” groups as they typically give a hydrogen atom to the isocyanate nitrogen to form a urethane. For example, at a base level, an alcohol includes an active hydrogen and reacts with isocyanate to form a compound as shown below:

Billions of pounds of polyols are used each year to manufacture polyurethanes. Most of these polyols are polyether polyols derived from fossil fuels, typically polyethylene oxide or polypropylene oxide based polyols. As the price of oil has increased, so has the price of polyether polyols. Therefore, it has become more desirable to explore alternative sources of polyols, including agriculturally derived products such as plant oils.
Plant oils are primary metabolites of many higher plants that are economically important as sources of food and industrial oils. Chemically, plant oils are triglycerides of mixes of fatty acids, which may be the same fatty acid or different fatty acids. Typically, plant oils contain some unsaturated fatty acids. Soybean oil, for example, contains about 54 wt. % linoleic acid, 23 wt. % oleic acid, 10 wt. % palmitic acid, 8 wt. % linolenic acid and 5 wt. % stearic acid. On average, soybean oil contains 4.65 sites of unsaturation (olefin groups, carbon-carbon double bonds) per molecule. If active hydrogen functional groups, such as alcohols, are introduced into the molecule of plant oil, the product can be used as a polyol to make polyurethane.
Many plant oils, such as corn oil, soybean oil, rapeseed oil, sunflower oil, peanut oil, safflower oil, olive oil, and cotton seed oil exist in abundant supply. This abundance may yield low cost polyols, if the plant oils could be functionalized with active hydrogen groups, such as alcohols, without the problems normally inherent in the epoxide synthetic pathway currently used in the production of most plant polyols. For example, almost all of the commercially available polyols made from soybean oil are manufactured in a two step process beginning with the epoxidation of soybean oil. Such process is well known in the art, and may be shown as follows:

In the above-identified pathway, hydroxyl groups are introduced onto the molecule of soybean oil in the second process step by opening the oxirane of epoxidized soybean oil to form soy polyol. This may be accomplished in a variety of ways. For example, U.S. Pat. No. 2,882,249 describes the soy polyol formed by ring opening epoxidized soybean oil with ricinoleic acid. U.S. Pat. No. 4,025,477 describes the soy polyol obtained by ring opening epoxidized soybean oil with acrylic acid. U.S. Pat. Nos. 5,266,714 and 5,302,626 describe soy polyols obtained by ring opening epoxidized soybean oil with carboxylic acids. U.S. Pat. No. 6,891,053 describes the soy polyol obtained by ring opening epoxidized soybean oil with acid leached clay. U.S. Pat. Nos. 4,508,853 and 4,742,087 describe the soy polyol obtained by ring opening epoxidized soybean oil with alcohols. U.S. Pat. Nos. 6,433,125 and 4,551,517 describe soy polyols obtained by ring opening epoxidized soybean oil with higher alcohols. U.S. Pat. No. 4,886,893 describes the soy polyol obtained by ring opening epoxidized soybean oil with polyfunctional alcohols. U.S. Pat. Nos. 6,107,433, 6,433,121, 6,573,354 and 6,686,435 describe the soy polyols obtained by ring opening epoxidized soybean oil with a mixture of water, alcohol and fluoroboric acid.
Epoxidized soybean oils used to manufacture soy polyols typically have epoxide numbers of from about 4.8 to about 7.2. If the epoxide number of epoxidized soybean oil is too low, the hydroxylation reaction will give a soy polyol that contains an undesirable concentration of by-products having zero and mono hydroxy group molecules. Soy polyol containing zero and mono hydroxyl group molecules result in polyurethanes with poor physical properties. If the epoxide number of the epoxidized soybean oil is too high, the hydroxylation reaction will produce a soy polyol product that contains an undesirably large concentration of by-product having intramolecular cross-linked molecules. High concentrations of by-products containing intramolecular cross-linking unacceptably increases the viscosity of the soy polyols as well as detrimentally affecting the physical properties of the polyurethane products. It is known in the art that ring opening, for example, via hydroxylation of epoxidized plant oils, results in a variety of complex by-products, including, but not limited to intra-molecular cross-linked by-products, intermolecular cross-linked by-products, hydrolysis by-products and alcohol exchange by-products. Furthermore, even the expected or planned products of epoxidized plant oils may be poor reactors, such as secondary hydroxyl groups in the middle of fatty acid chains, which may be high in stearic hindrance.
Currently, manufacturers seeking to use plant oil polyols, such as soybean oil-derived polyols, to produce polyurethane, typically must choose between inexpensive, high viscosity raw materials that are dark in color or, alternatively, expensive, low viscosity and lighter colored materials. Products from both materials may have poor physical properties that limit market acceptance. Furthermore, such poor properties may limit the overall percentage in which such materials are added to polyurethane formulations. For many uses, preferably, a plant polyol reactant would be a low cost, low viscosity and light colored raw material comparable to certain materials derived from fossil fuels. However, because of the problems inherent in opening the epoxide ring of epoxidized plant oils, such as epoxidized soybean oil, such physical properties are not possible with the currently available technology.
It is noted that it is known in the art to hydroxylate hydrocarbons by biological methods. However, to date, known processes have proven uneconomical. Also, some plant oils can be used as polyols without modification. For example, castor oil contains on average about 2.7 hydroxyl groups per molecule. However, the supply of castor oil is limited and properties of polyurethanes made from such polyols (such as resilience) are not equal to those of fossil fuel derived materials.
Certain polyols may be derived from plant sources. For example polytetramethylene glycol (PTMEG) is derived from polymerizing tetrahydrofuran (THF) from corn. Such polyols yield polyurethanes with excellent physical properties and are thus superior raw materials. However, to date, the high cost of producing such polyols has resulted in limited market acceptance.
It is noted that Gast et al., U.S. Pat. No. 3,485,779 (hereafter Gast) discloses reactions of hydroxylamines with triglycerides. Specifically, Gast discloses that linseed and soybean N,N-bis-hydroxyalkyl fatty amides can be obtained by a strong base sodium methoxide catalyzed aminolysis of linseed oil and soybean oil. Such a reaction may be set forth as follows:

Schneider et al., U.S. Pat. No. 4,094,838 discloses soybean N,N,-bis-hydroxy ethyl fatty amide that can be used to make water-dispersible polyurethane coatings as a small molecule polyol of polyurethane resin. Schneider teaches diethanolamine as a preferred amidating agent in a base catalyzed aminolysis. The preferred catalyst being sodium methoxide.